Th. Böhm, the inventor of the modern flute modernized almost every component of the instrument, but he kept unchanged the tuning plug disposed in the flute headjoint and the crown adapted to close off the flute headjoint. The tuning plug is typically made of cork—even in the most expensive handmade instruments—with a plate made typically of metal being added to it by most manufacturers. The sound quality of the flute primarily depends on the quality of the headjoint.
Due to the presence of the cork, the left-hand side of the flute headjoint is an acoustically passive “mute” pipe section. The heart of the instrument is the sonic chamber situated under the embouchure hole. The sonic chamber is a region of the headjoint approximately 4 cm across, with the sound propagating from the centre thereof towards the open end of the pipe. Due to the material of the tuning plug the left-hand side of the headjoint is acoustically inoperative in its conventional state, the instrument therefore emitting sound in the forward and right-hand directions. A material characteristic of cork is that it absorbs a fraction of sounds and oscillations.
Efforts have been made to eliminate the disadvantages caused by the cork material. Thus, the patent description U.S. Pat. No. 6,660,919 discloses a solution wherein the closed crown, the screw shaft and tuning plate, together with a portion of the cork, are retained. The stable retention of the tuning plug is provided by an additional insert adapted for receiving the screw shaft, which metal insert improves the sound of the flute, albeit to a small extent.
This solution has the disadvantage that the upper pipe section still remains muffled by the cork and the closed-off tuning plug.
Since 2012 the Japanese flute maker Nagahara has been selling such flute headjoints wherein a plug and balance weight made for silver headjoints are applied, with the customers being able to choose the components that best suit their needs. Although this configuration facilitates the use of the instrument, the closed crown and the cork muffle the sound.
Other solutions applying replaceable tuning plugs but retaining the cork inside the headjoint are also known.
Robert Bigio was the first flute maker to completely discard cork and to apply a metal tuning plug with a closed crown. He built the balance weight into the crown.
The disadvantage of his design is that the tuning plate still has a flat face.
The objective of the present invention is to provide a flute headjoint that eliminates the disadvantages of conventional headjoints, namely that                the flat tuning face applied inside the flute headjoint is less suitable for notes with accidentals,        when played softly, the flute typically sounds flat, while it is usually sharp when played loudly,        high-pitch notes are unstable, their resonance being unable to sustain a clear tone, and therefore constant pitch compensation is required,        low-pitch notes are difficult to play in a forte passage, while high-pitch notes have to be blown strongly, which strains the concentration of the player,        conventional flutes emit sound only in the forward and right-hand directions.        
The present invention is based on the recognition that by applying a three-dimensional, concave tuning surface instead of a flat surface an improved, clearer sound can be achieved. With an open crown the flute also emits sound in the left-hand direction.